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Authors: Zhang, Minghui
Advisor: Pöschl, Ulrich
Title: Development of an in situ laser-induced fluorescence spectrometer for real-time analysis of bioaerosols
Online publication date: 25-Jul-2022
Year of first publication: 2022
Language: english
Abstract: Characteristic particle size, fluorescence intensity and fluorescence spectra are important features to detect and categorize bioaerosols. In this thesis, I developed a size-resolved single-particle fluorescence spectrometer (S2FS), which enables measurement of fluorescence spectra dispersed in 512 channels between 370 nm and 610 nm with excitation wavelength (λex) at 355 nm. Moreover, it can simultaneously measure aerodynamic diameters of aerosol particles from 0.5 μm to 20 μm (52 channels, logarithmic size scale). The S2FS consists of an aerodynamic particle sizer and a fluorescence spectrometer with a 355-nm laser excitation source and an intensified charge-coupled device (ICCD) as detector. Preliminary ambient measurement in Mainz (Germany, central Europe) show that an emission peak at ~440 nm was frequently observed for fluorescent fine particles (0.5-1 μm), suggesting the occurrence of dipicolinic acid (DPA), which constitutes a significant fraction of bacterial endospores and exists exclusively in bacterial endospores. Fluorescent fine particles accounted for 2.8% on average, based on the number fraction in the fine mode. Fluorescence coarse particles (> 1 μm) exhibited emission peaks at ~440 nm, ~450 nm, and ~470 nm, suggesting the existence of agglomerated bacterial endospores, pollen fragments, and fungal spores in the coarse mode. Fluorescent coarse particles accounted for 8.9% on average based on the number fraction, with strongest occurrence observed during a thunderstorm and in the morning. I further demonstrate that the volume of the single particle can be used as the single parameter to calibrate the intensity of online/in situ fluorescence spectrometers (OFS). Among the materials tested, nicotinamide adenine dinucleotide (NADH), cellulose, and chitin exhibit fluorescence scaling with the volume of the particle. After the fluorescence intensity is calibrated by volume, the fluorescence spectra are nearly the same for particles with different sizes. This method implies that the fluorescence intensity can be compared and scaled between different online/in situ fluorescence spectrometers. The last part is to explore the potential interference of biogenic secondary organic aerosols (SOA). I measured the fluorescence property of fresh SOA and aged SOA in the particle phase by using the S2FS. Fresh SOA were generated by the reaction of limonene or α-pinene with ozone (O3) while aged SOA were generated by the reaction of limonene or α-pinene with ozone (O3) in the presence of ammonia. Preliminary results show that fresh SOA exhibit fluorescence from 400-500 nm with the emission peaking at ~470 nm while aged SOA cover a broader range from 400-610 nm with the emission peaking at ~480 nm with λex = 355 nm. The fractions of fluorescent fresh SOA and fluorescent aged SOA are 1-4% and 6-10%, respectively. Relative humidity (RH) influences fluorescence of fresh SOA in the shorter wavelength while RH influences fluorescence aged SOA mainly in the longer wavelength.
DDC: 540 Chemie
540 Chemistry and allied sciences
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
Place: Mainz
URN: urn:nbn:de:hebis:77-openscience-756ea16a-d3e8-45cd-88be-e8162d95eeb55
Version: Original work
Publication type: Dissertation
License: CC BY
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Extent: IV, 120 Seiten, Illustrationen, Diagramme
Appears in collections:JGU-Publikationen

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